<iframe src=<%= @room.monitor_link.present? ?  @room.monitor_link : "http://" %> frameborder="0"></iframe>

<script type="text/javascript">
  $(function(){
    cWidth = $('body').width() - 220 + "px";
    cHeight = $('body').height() + "px";
    $("iframe").css({"width":cWidth, "height":cHeight});
  })
</script>